WORMS. 311 



this edge, and as it were imbedded into it for about 

 one-third of their length, are set between seventy and 

 eighty crystalline points, of highly refractive substance, 

 resembling glass. Tliese points gradually decrease in 

 size towards one end of the series, and at length cease, 

 leaving a portion of the cutting edge toothless. At the 

 end where they are largest, they are nearly close to- 

 gether, but at length are separated by spaces equal to 

 their own thickness. The manner in which they are 

 inserted closely resembles, in this aspect, the im- 

 plantation of the teeth in the jaw of a dolphin or croco- 

 dile. 



But this appearance is illusory. By affixing the 

 little jaw to the revolving needle, we bring the edge to 

 face our eye. It is not an edge at all ; but a narrow 

 parallel-sided margin of considerable breadth. And 

 the teeth are not conical points, as they seemed when 

 we viewed them sidewise, but flat triangular plates, 

 with a deep notch in their lower edge. Thus they 

 partly embrace, and are partly inserted in, the margin 

 of the jaw. 



Observe now how beautifully this apparatus sub- 

 serves the purpose for which 

 it is intended. By means of 

 its sucker, the Leech creates »S' 



a vacuum upon a certain part ^ .« ^ , vV 

 of the skin, exactly like that ^ \[^'' '■•*''* ' ' ' i 

 produced by a cupping-glass. ^ •]i^j§^''r'i'''| . J 

 The skin covered is drawn in- ^ * \ '{,''' 'I'i'i' 

 to the hollow so far as to ren- 

 der it quite tense, by the jaw of mech (fe part). 

 pressure of the surrounding air. Thus it is brought 

 into contact with the edges of the three jaws, to which, 



